Hard material bit

ABSTRACT

A hard material bit for a drilling head ( 2 ) includes at least two cutting edges ( 4   a   , 4   b ) over a bit length (L) in a direction transverse to a bit drilling axis (A), with one of the at least two cutting edges ( 4   a ) being located adjacent to a first side surface ( 5   a ) of the bit and another of the at least two cutting edges being located adjacent to the second side surface ( 5   b ) of the bit spaced form the first side surface ( 5   a ) by a thickness (D), the bit further including a base surface ( 6 ) located opposite the cutting edges ( 4   a   , 4   b ) at a height (H) along the drilling axis (A), and two recesses ( 7   a   , 7   b ) formed in respective longitudinal portions of the base surface ( 6 ) located opposite the one and the another of the at least two cutting edges ( 4   a   , 4   b ), respectively, and extending up to the first and second side surfaces ( 5   a   , 5   b ), respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chisel-shaped hard material bit for a rock drilling head, in particular, for an injection self-drilling anchor.

2. Description of the Prior Art

Such mass-produced drilling heads have, at a width across comers between 25 and 60 mm, a low degree of complexity. Because injection self-drilling anchors are needed in large quantities, their effective and material-saving manufacturing become of great importance. A forked drilling head with two prong-shaped free-standing plate carriers and a brazed therewith plate-shaped hard-material insert that forms a chisel-shaped cutter with cutting edges and inclined cutting surfaces, proved to be effective.

Chisel-shaped hard material bits are usually formed as hard material plates with two cutters diametrically arranged relative to each other in a gable-shaped manner. During the manufacturing process of the hard material plates by sintering, in order to form a blank, the powder is compressed in a press-mold under a high pressure in a direction normal to side surfaces. As a result of a flow process in the press mold, a hydrodynamic pressure distribution takes place in the powder which gives the hard material plate its geometry. The flow processes greatly affect the homogeneity of the powder distribution and, thereby, the quality of a produced sintered component, in particular, in the edge regions, which form in the hard material plate which are used as chisel-shaped hard material bits, the highly stressed cutting edges. The not sufficiently dense or not completely formed cutting edges lead to formation of crack-initiating notches. Therefore, the geometry of the hard material plate, which is obtained as a result of a flow process during pressing of blanks, greatly influences the usable life of the produced hard material bit.

German Publication DE 28 02 119 discloses a drilling head with a brazed plate-shaped hard material insert that forms a chisel-shaped bit. A base surface that is located opposite the centrally arranged cutting edge, is formed of two, inclined toward each sections which are connected with the side surfaces of the bit by rounded transition regions.

U.S. Pat. No. 5,464,068 discloses a drilling head including a hard material cutting plate formed of a CVD-diamond, having a small height and two cutting edges extending at angle to each other, forming a gable-shaped profile, with a concave base surface extending transverse to the side surfaces.

British Patent No. 971,971 discloses a thick hard material cutting plate the base surface of which is beveled at both sides and the central cutting edge of which has on each of its opposite sides a concave trough, whereby the cutting plate becomes thinner in the cutting edge region.

International Publication WO 2004 02 72 06 discloses a hard material cutting plate the base surface of which has a concave recess in which a wing of a prong-shaped plate carrier of a forked drilling head fittingly engages. The recess is located on the side of the cutting edge.

U.S. Pat. No. 4,489,798 discloses a thin hard material cutting plate (the thickness amounts to tenths of the length) having along its longitudinal extent two cutting edges arranged in a gable-shaped manner relative to each other, and having different side surfaces and also side cutting edges.

An object of the present invention is to provide a chisel-shaped hard material bit formed of a sintered material and which would insure saving of material during its manufacturing and an extended service life of the drilling head in which the hard material bit is used.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a hard material bit including at least two cutting edges over a bit length in a direction transverse to a bit drilling axis, a first side surface and a second side surface spaced from the first side surface by a thickness of the bit, with one of the at least two cutting edges being located adjacent to the first side surface and another of the at least two cutting edges being located adjacent to the second side surface, a base surface located opposite the cutting edges at a height along the drilling axis, and two recesses formed in respective longitudinal portions of the base surface located opposite the one of the at least two cutting edges and the another of the at least two cutting edges, respectively, and extending up to the first and second side surfaces, respectively.

As a result of formation of recesses in the base surface, on the side surfaces of the cutting edges, during pressing of a blank, a shear pressure in a direction of the cutting edges and normal to the side surfaces is generated. This shear pressure strengthens, as a result of the associated shear flow, the powder in the direction of the cutting edges, leading to homogenous and dense powder distribution there. This prevents appearance of potential crack-initiating notches in the cutting edges. With two recesses associated with cutting edges, distributed over the base surface length and associated with different side surfaces, both partial pressures, which have a different orientation relative to the thickness, are adequately separated from each other and do not cancel each other. As a result, there is provided a hard material bit produced sintering with a significant saving of material and having a satisfactory service life.

Advantageously, the cutting edges are formed directly on the side surfaces, which makes them particularly sharp.

Advantageously, the recess volume (measured with respect to a base brazing surface extending transverse to the side surface) amounts to between a half and a double of, advantageously, to a single of a cutting volume (measured with respect to a counter-edge brazing surface). Thereby, in the sense of a continuous balance, accumulation of additional powder volume on the base surface is prevented.

Advantageously, a cross-section across a middle portion of a cutting edge has essentially a shape of a parallelogram limited by the two, parallel to each other side surfaces and by likewise parallel, cutting surface and base surface both of which extend, respectively, at an acute free angle to a horizontal. Because a parallelogram, as known, is formed by shearing of a rectangle, during the flow process, homogeneously distributed infinitesimal shear deformation are sufficient for a complete filling of the cross-section, without an extended transportation of powder.

Advantageously, both the thickness and the height amounts to less than a third, advantageously, to a fourth of the bit length, which permits to form a material-saving bit. The associated with this, reduction of the cross-section increases the flexibility of the hard material bit along its length that defines a bore cross-width. In addition, a low height of the hard material bit reduces the latent stress within the brazing layer, which is produced, during brazing of the bit with the drilling head, as a result of different expansion coefficients. Thereby, the loading capability of the hard material bit and the drilling head increases.

Advantageously, the base surface is formed as a concave surface over its length, whereby with the cutting edges forming a gable-shaped structure along the bit length, an angular hard material bit with a reduced central height is formed, which further contributes to saving of a material.

Advantageously, the recesses are limited in the longitudinal direction at their opposite sides. Thereby, during pressing, there is generated, on the longitudinal boundary of the hard material bit, a shear component in a direction of a side cutting edge which must have, in injection self-drilling anchors in particular, a long service life for retaining the dimensional accuracy of the bore cross-width.

Advantageously, as it has already been discussed, an inventive hard material bit is used in drilling heads of injection self-drilling anchors. Because such anchors are mass-produced, the bit proved to be particularly effective in such one-time usable products, permitting a big saving of material.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 a side view of a hard material bit according to the present invention as viewed from plane I-I in FIG. 2; and

FIG. 2 a cross-sectional view through a middle portion of a cutting edge along plane I-I in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a chisel-shaped hard material bit 1 for a forked drilling head 2 which is shown in FIG. 1 schematically with dash lines and is designed for use with an injection self-drilling anchor 3. The bit 1 has, over its length L of 60 mm and measured in a direction perpendicular to its drilling axis A, two cutting edges 4 a and 4 b arranged in a gable-shaped manner. The cutting edges 4 a and 4 b are formed on different, spaced by a thickness D of 3 mm, side surfaces 5 a, 5 b. Each of respective cutting edges 4 a, 4 b is associated with a recess 7 a, 7 b formed in an opposite longitudinal portion of a base surface 6 of the bit 1 at a height of 8 mm from the cutting edge 4 a, 4 b. The recess 7 a, 7 b is limited at its opposite sides and extends precisely up to the side surface 5 a, 5 b that forms the cutting edge 4 a, 4 b. The base surface 6 itself is formed along its length L as a concave surface. The cutting edges 4 a, 4 b pass on the respective side surfaces 5 a, 5 b into respective side cutting edges 11 a, 11 b.

According to FIG. 2, the recess volume VA measured with respect to a basic brazing surface 8, which extends transverse to the side surface 5 a, is the same as the cutting edge volume VS measured with respect to an opposite edge brazing surface 9 likewise extending transverse to the side surface 5 a. The cross-section itself has a shape of essentially a parallelogram limited by the parallel to each other side surfaces 5 a, 5 b and by likewise parallel to each other cutting surface 10 and the base surface 6 that extend at an acute free angle α.

Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. A hard material bit for a drilling head (2), comprising at least two cutting edges (4 a, 4 b) over a bit length (L) in a direction transverse to a bit drilling axis (A); a first side surface (5 a) and a second side surface (5 b) spaced from the first side surface (5 a) by a thickness (D), one of the at least two cutting edges (4 a) being located adjacent to the first side surface (5 a) and another of the at least two cutting edges being located adjacent to the second side surface (5 b); a base surface (6) located opposite the cutting edges (4 a, 4 b) at a height (H) along the drilling axis (A); and two recesses (7 a, 7 b) formed in respective longitudinal portions of the base surface (6) located opposite the one of the at least two cutting edges (4 a) and the another of the at least two cutting edges (4 b), respectively, and extending up to the first and second side surfaces (5 a, 5 b), respectively, which is close to the cutting edge (4 a, 4 b).
 2. A hard material bit according to claim 1, wherein the one and another cutting edges (4 a, 4 b) are formed directly on the first and second side surfaces (5 a, 5 b), respectively.
 3. A hard material bit according to claim 1, wherein a recess volume (VA) amounts to between a half and a double of a cutting edge volume (VS).
 4. A hard material bit according to claim 1, wherein a cross-section across a middle portion of each of the at least two cutting edges (4 a, 4 b) has a shape of essentially a parallelogram.
 5. A hard material bit according to claim 1, wherein both the thickness (D) and the height (H) amount to less than a third of the length (L).
 6. A hard material bit according to claim 1, wherein the base surface (6) is formed over the length (L) as a concave surface.
 7. A hard material bit according to claim 1, wherein each of the two recesses (7 a, 7 b) is limited in a longitudinal direction thereof at opposite sides thereof. 